Many studies have been made so far on methods for hydrogenating an aromatic carboxylic acid in the presence of a noble metal catalyst, and catalysts used in the methods. Now, regarding a method for directly hydrogenating an aromatic ring of an aromatic carboxylic acid, many studies are being made on rhodium catalysts with which the hydrogenation reaction proceeds under mild conditions (Non Patent Literature 1, Non Patent Literature 2, Patent Literature 1, and Patent Literature 2). Rhodium catalysts have advantages such as a high activity as a catalyst for hydrogenating an aromatic carboxylic acid and a high selectivity to a product without occurrence of any side reaction. Rhodium has such excellent catalytic performances, but has several problems in industrial use. A first problem is its very high price, and this imposes a heavy load of initial investment in the catalyst for industrial use. A second problem is that the degradation speed of the activity of the catalyst is so high that frequent activation operation is required for long-term use of the catalyst. Although a process incorporating activation can be created, a simpler process is desired for industrial use (Patent Literature 1).
Ruthenium is one of the inexpensive noble metals having an ability to hydrogenate an aromatic carboxylic acid. It is generally known that when a ruthenium catalyst is used for hydrogenating an aromatic carboxylic acid, not only hydrogenation of the aromatic ring occurs, but also reduction of the carboxyl group as the side chain occurs. Hence, the selectivity to an alicyclic carboxylic acid decreases. Also from the fact that ruthenium catalysts are also used as reduction catalysts of a carboxyl group to an alcohol, the decrease in selectivity is obvious (Non Patent Literature 3). It is known that the use of a ruthenium catalyst for hydrogenation of an aromatic carboxylic acid requires conversion of the carboxylic acid to an ester, and such a process involves two additional steps including esterification of the aromatic carboxylic acid and hydrolysis for the alicyclic carboxylic acid (Patent Literature 3 and Patent Literature 4). Similarly, it is known that the use of a ruthenium catalyst for hydrogenation of an aromatic carboxylic acid requires conversion of the carboxylic acid to an inorganic salt such as a sodium salt, and such a process involves two additional steps including derivation of the inorganic salt from the aromatic carboxylic acid, and desalination of the inorganic salt of the alicyclic carboxylic acid.